The known conventional particle ejecting pump in a coating device in which particles are fed out along with gas from a coating gun nozzle is, for example, constructed as shown in FIG. 12. More specifically, a porous plate 2 on which particles to be coated are placed is provided at a lower portion of a particle feed tank 7. The porous plate 2 is provided with a straight particle feed tube 8, one end of which is opened to the porous plate 2 and the other end of which is connected to an ejector 9. In the pump of such a construction, particles 1 are fed to upside of the porous plate 2, and fluidizing air 6 fed to the downside of the particle feed tank 7 passes through the porous plate 2 and agitates the particles 1 on the porous plate 2. Further, the particles 1 are fed to the ejector 9 via the particle feed tube 8 by an internal pressure Pa in the particle feed tank 7. Other similar examples are disclosed in Japanese Patent Laid-Open Publications No. 6-286872 and 6-304502.
Such a conventional particle-coated substrate fabricating apparatus has had the following problems. Even if a proper particle size distribution of the particles 1 is obtained by agitating the particles 1 so that it is brought into a fluidized state on the porous plate 2 (hereinafter, the term "agitation" means an agitation for imparting a fluidized state), the particles 1 would be subject to blocking, agglomeration or bridging again inside the particle feed tube 8 and in the container of the ejector 9 so that the particle size of the particle would be coarsened. The above "bridging" means that supplying particles are adhered in a certain range of size. The above "blocking" means that the bridging particles are adhered to each other and agglomerate. As a result, even if the particles 1 undergo shear due to a gas stream 5 fed to the ejector 9, the particles 1 would agglomerate and thereby have a coarsened particle size and a varied particle size distribution. Consequently, the conventional coating device has had difficulty in ejecting fine particles having a particle size distribution of 5 .mu.m or less without agglomeration. Furthermore, even if the particles 1 have a relatively large particle size, its particle size distribution would vary with time, encountering difficulty in controlling the particle size.
The object of the present invention is, therefore, to remedy the above-described disadvantages and to provide a particle ejector capable of attaining a uniform particle size distribution, a particle-coated substrate fabricating apparatus comprising the ejector, a particle-coated substrate fabricating method, a particle-coated substrate and a coated abrasive sheet having a uniform particle size distribution. While the present invention advantageously overcomes the problems described above with spraying particles of 5 .mu.m or less, the present invention is not thereby limited and may of course also be advantageously used with particles larger than 5 .mu.m.